Investments In Unconsolidated Joint Ventures (Narrative) (Details)
ft² in Millions
 3 Months Ended 6 Months Ended
Jun. 01, 2015
USD ($)
item
May. 13, 2015
USD ($)
item
Jun. 30, 2015
USD ($)
ft²
property
item
Jun. 30, 2014
USD ($)
Jun. 30, 2015
USD ($)
ft²
property
item
Jun. 30, 2014
USD ($)
Dec. 31, 2014
USD ($)
Schedule of Equity Method Investments [Line Items]              
Company's investments in unconsolidated joint ventures, net     $ 284,507,000   $ 284,507,000   $ 247,468,000
Management, leasing, development and other services fees     1,400,000 $ 1,400,000 3,100,000 $ 2,800,000  
Accounts receivable due from unconsolidated joint ventures     800,000   800,000   1,000,000
Maximum exposure to loss     206,100,000   206,100,000    
Estimated future funding commitments     51,800,000   51,800,000    
Realized gains on dispositions, net     $ 34,399,000 $ 54,584,000 $ 34,543,000 $ 54,584,000  
Unconsolidated Joint Venture Office Buildings [Member]              
Schedule of Equity Method Investments [Line Items]              
Number of properties | property     36   36    
Unconsolidated Joint Venture Office And Retail Buildings [Member]              
Schedule of Equity Method Investments [Line Items]              
Area of property (in square feet) | ft²     5.7   5.7    
Unconsolidated Joint Venture Retail Buildings [Member]              
Schedule of Equity Method Investments [Line Items]              
Number of properties | property     2   2    
Unconsolidated Joint Venture Multi-Family Properties [Member]              
Schedule of Equity Method Investments [Line Items]              
Number of properties | property     13   13    
Number of units | item     4,343   4,343    
Unconsolidated Joint Venture Hotel [Member]              
Schedule of Equity Method Investments [Line Items]              
Number of units | item     350   350    
Unconsolidated Joint Venture Development Projects [Member]              
Schedule of Equity Method Investments [Line Items]              
Number of units | item     1,074   1,074    
Unconsolidated Joint Venture Land Parcels [Member]              
Schedule of Equity Method Investments [Line Items]              
Number of units | item     2,910   2,910    
Unconsolidated Joint Ventures [Member] | Guarantee of Indebtedness of Others [Member]              
Schedule of Equity Method Investments [Line Items]              
Maximum borrowing capacity     $ 477,000,000   $ 477,000,000    
Amount outstanding     263,600,000   263,600,000    
Unconsolidated Joint Ventures [Member] | Parent Company [Member] | Guarantee of Indebtedness of Others [Member]              
Schedule of Equity Method Investments [Line Items]              
Maximum borrowing capacity     67,800,000   67,800,000    
Amount outstanding     $ 36,900,000   $ 36,900,000    
Minimum [Member]              
Schedule of Equity Method Investments [Line Items]              
Percentage of interest in venture     7.50%   7.50%    
Maximum [Member]              
Schedule of Equity Method Investments [Line Items]              
Percentage of interest in venture     85.00%   85.00%    
Variable Interest Entity [Member]              
Schedule of Equity Method Investments [Line Items]              
Company's investments in unconsolidated joint ventures, net     $ 154,300,000   $ 154,300,000    
Number of VIEs | property     9   9    
Office [Member] | Unconsolidated Joint Venture Land Parcels [Member]              
Schedule of Equity Method Investments [Line Items]              
Area of property (in square feet) | ft²     1.4   1.4    
South Pier At Harborside [Member]              
Schedule of Equity Method Investments [Line Items]              
Company's investments in unconsolidated joint ventures, net [1]              
Number of units | item     350   350    
Percentage of interest in venture [2]     50.00%   50.00%    
Letter of credit     $ 4,100,000   $ 4,100,000    
Overlook Ridge JV, L.L.C. [Member]              
Schedule of Equity Method Investments [Line Items]              
Number of units | item   251          
Percentage of interest in venture   50.00%          
Amount sold   $ 74,600,000          
Distributed cash received from sale   0          
Realized gains on dispositions, net   $ 0          
Rosewood Lafayette Holdings, L.L.C. [Member]              
Schedule of Equity Method Investments [Line Items]              
Company's investments in unconsolidated joint ventures, net [3]             $ 62,000
Number of units | item 217   217 [3]   217 [3]    
Percentage of interest in venture 25.00%   25.00% [2],[3]   25.00% [2],[3]    
Realized gains on dispositions, net $ 6,400,000            
[1] The negative carrying amount for this venture of $2,570 and $1,854 as of June 30, 2015 and December 31, 2014, respectively, were included in accounts payable, accrued expenses and other liabilities.
[2] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.
[3] See discussion in Recent Transactions following in this footnote for disposition of Company's interest in the unconsolidated joint ventures.